2.2I: Covalent Network Structure

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What are Covalent Network Structures?

giant 3D network of atoms linked by covalent bonds

What are Allotropes?

elements with different bonding and structural patterns, and so have different physical and chemical properties (e.g. O2 and O3)

What are the 4 allotropes of carbon?

1. Diamond

2. Graphite

3. Graphenes

4. Fullerenes

Tell me about Diamonds

each carbon shares electrons with 4 other carbons (tetrahedral)

• high melting points

• very hard

• non-conductive

• Insoluble in H2O

Tell me about Graphite

• Layered structure, sheets attract one another through L.D. forces

• Each carbon bonds with 3 other carbons

• Remaining electron is “spare”, can become delocalized

  • High melting point

  • soft, slippery feel

  • Insoluble in H2O

  • Conducts electricity

Tell me about Graphene

like graphite but single-layer only

• Conducts electricity

• Conducts heat

• Very flexible

• High melting point

Tell me about Fullerene (C₆₀)

Each carbon bonds with 3 others to form a sphere

• Semi-conductor

• low thermal conductivity

• Low melting point

Tell me about Silicon Dioxide

• has 4 valence electrons

• Silicon dioxide forms covalent network structures

• Oxygen acts like bridge connecting silicon atoms

• High melting point

• Hard

• Non-conductive

• insoluble